Grinding



C. GUMPER March 12, 1946.

GRINDING Filed Jun 22, 1943 J? 6' --2 q y /L3/ 2 INVENTOR 25d 6 ar nae 6202130);

y ATTORNEYS Patented Mar. 12, 1946 GRINDING Clarence Gumper, West Haven, Conn, assignor to The Bridgeport Safety Emery Wheel Company, Inc., Stratford, Conn, a corporation of Connecticut Application June 22, 1943, Serial No. 491,750 4 Claims. (01. 51289) This invention relates to grinding, and more particularly to grinding of relatively soft or re silient materials.

Many times it is desired to grind cylindrical articles so as to finish or partially finish the external or peripheral surface thereof, or to reduce the article to a desired diameter.

In the grinding of rubber and rubber-like articles, great difficulty has long been encountered, for with such articles an excessive amount of heat is developed not only by the friction produced between the grinding wheel and the article but also by the energy consumed as a result of the progressive distortion or displacement of the relatively soft material by the grinding wheel as the latter is traveled along the rotating article to be ground. This excessive amount of heat results in burning or partially melting the article and causes the grinding wheel to deteriorate rapidly, requiring it to be frequently dressed and permitting its use for only a rela-- tively short time.

In addition to developing excessive heat, the drawing or distortion of the material of the article in the direction of the cut produces a hump which, becoming excessive, suddenly passes under the wheel. This causes the wheel and article to chatter, leaving undesirable, rough and uneven surfaces on the article as evidenced by a discernible pattern produced on the surface thereof. 7

Another difficulty has been that in grinding interrupted or broken cylindrical surfaces such as a disk with projections very much like gear teeth, itfrequently occurred that although the grinding wheel was properly adjusted for successfully performing the operation on a number of pieces, it was not infrequent that the grinding wheel would bite into the projections and knock or rip them off, thus spoiling the piece. This happens most frequently when the article is made of a harder or less resilient rubber or rubber-like composition.

It has been the practice heretofore to employ a wheel of reasonable width considering the amount of material to be removed from the article to be ground and the ability of the wheel to withstand the centrifugal force tending to disintegrate it at the high speeds at which such wheels are unnecessarily operated. It has been thought that the use of a narrower wheel, to reduce the operative width of the grinding Wheel and thus the number of abrasive grits which may be operative on the article to be ground at one time, would result in a slower and less efficient grinding operation, and this is probably true with regard to conventional grinding wheels. The use of a narrower wheel did not solve the problem, for it left the surface of the article patterned by rough uneven surfaces.

However, the difficulties above referred to have been solved by the present invention by provid-' ing a grinding wheel of essentially the same width as conventional grinding wheels used for the same purpose, but having its grinding surface interrupted or divided by a space so as to form two (or more in the event that more than one space is provided) grinding surfaces to be presented seriatim to the article to be ground as the work progresses. I have found that when the grinding wheel is so divided, notwithstanding the fact that both surfaces operate in the same plane, the

' leading grinding surface removes the larger quantity of material to be ground off during the traverse of the work by the grinding wheel, and does so without excessivedrawing of the material being ground, 'and that whatever stress is present in the material, as a result of the grinding operation by the leading grinding surface,

it is relieved at the space between the two grinding sections so that the material resumes its normal position, leaving to the second grinding surface the comparatively light work of finish grinding, that is to say, smoothing off the chatter marks caused by the first grinding surface; and that the material after the second grinding surface has passed over it is comparatively smooth and free of any irregularities such as an objectionable pattern of chatter marks.

I have found that the dividing groove may be quite narrow without reducing the eflicacious operation of the wheel. For instance, I have found that with a 10" diameter wheel having a width from edge to edge of 1", the groove may be only wide to obtain the desired results as above stated.

The groove may have any desired depth depending upon the amount which the wheel may be worn or dressed off before it is discarded and depending upon the strength of the bonding medium in the wheel to resist disintegration of the narrowed wheel sections due to the centrifugal force developed at the high speeds at which such grinding wheels are used. 'With the particular composition which I employ which has a Bakelite base, I have found that the groove in a 10" wheel such as above described may be at least 1 deep.

In the operation of the wheel of the present invention, when taking a cut of the same depth as would be done with a conventional wheel and which would then result in excessive overheating not only of the article being ground but also of the wheel and driving motor, it has been found unexpectedly that the temperature of the article being ground has not been substantially or excessively raised nor does the motor operate at a temperature higher than any other electric motor developing its full power. Likewise, the wheel is not excessively hot. ,In fact, the temperature of the article, the grinding wheel and the motor is such that the article being ground and the motor may be touched by the hand without danger of burning, an act which would be extremely dangerous with a conventional grinding wheel.

I do not have any definite or conclusive understanding as to the reason for the development of so little heat with the use of the wheel of the present invention. I simply know it to be a fact. One theory advanced is that since the distortion and displacement of th material being ground is relieved when the space between the two grinding surfaces is reached, less useless work is performed with the resulting development of less heat. The grinding wheel is usually employed in connection with a blower system which sucks in fresh air as well as the dust from the grinding operation. In view of this, another theory for the reduction of operating temperatures and thus the prolonging of the life of the wheel and the reduction of spoilage of the articles being ground, is that the work of grinding off the material is distributed between two grinding portions of the wheel which rotate in an atmosphere of continuously fresh air and having a groove between them radiate their heat more rapidly. However, experiments have not established either theory conclusively, and it may be that the reasons for the improved results obtained by the use of the wheel of the present invention is a combination of those above suggested and possibly some others as yet unknown.

The present invention may be applied in various sorts of ways to existing or conventional wheels and to wheels of various shapes and sizes, so long as the leading and trailing grinding surfaces operate in substantially the same plane.

In the accompanying drawing which illustrates one embodiment of this invention Figure 1 is a perspective view showing the wheel of the present invention applied to a conventional grinding machine.

Fig. 2 is an edge view of the grinding wheel.

Fig. 3 is a sectional view taken on line 3-3 of Fig. 2.

Fig. 4 is an edge view of a modified. form of this invention in which the wheel is provided with two annular grooves.

Fig. 5 is an edge view of a composite wheel made up of two separate wheels having between them the desired space.

Fig. 6 is an edge view of a conical wheel made according to the present invention.

As shown in the drawing, the grinding machine is provided with a mandrel connected by a dog H to a dog plate I 2 on a center carrying member l3 carried by a shaft l4 driven by a motor. The other end of the mandrel is engaged by a center IS on an adjustable center carrier I6 which is movable away from the mandrel so that the latter may be taken from the machine for the removal from, and application to, the mandrel of a tube I! of rubber or rubber-like material, the surface of which is to be ground.

The grinding wheel of the present invention is illustrated at l8. In this particular instance, it is mounted on the shaft of a motor l9 carried by a bracket 20 connected to a carriage not shown which may be fed longitudinally of the work by a suitable feed or travel mechanism, so that the wheel I8 is caused to traverse the work while being rotated by the motor I9 to remove surface portions from the rotating tube [1.

The wheel is provided with a suitable cover or hood 2| and a trough 22 which collects the particles ground-off the article I1. The trough 22 is connected to a suitable blower system to carry ofi the particles, and as a result fresh air is drawn into the trough 22 and past the adjacent surface of the wheel I8 as the grinding operation proceeds.

It should be understood, of course, that the above illustration and description is simply by Way of example, the example chosen being one in which extremely satisfactory and advantageous results have been obtained. Obviously, the present invention is not limited to the grinding of a tubular article as shown in Fig. 1, but any other article having complete or interrupted cylindrical surfaces may be ground.

The present invention is not in any way limited to the grinding of hollow articles, nor to soft and quite resilient material such as represented by the rubber tube illustrated in Fig. 1. However, the thinner or less rigid the article to be ground the greater the noticeable improvement resulting from the-present invention, at least so far as producing a smooth regular surface on the finished article is concerned. Nevertheless, with articles of harder composition in which the cylindrical surface is interrupted or broken, as by teeth-like portions, great improvement results from the use of this invention. Heretofore, it was not infrequent that with the use of the conventional grinding wheel, such projections were torn or ripped oil the work, thus spoiling the piece and resulting in loss of not only considerable material but also the labor expended to bring the article to the grinding stage.

As above explained, the advantageous results of the present invention are accomplished by interrupting the grinding surface of the wheel by providing therein an annular groove or a space between the two grinding surfaces.

Accordingly, as shown in Fig. 2, the grinding wheel l8 of the present invention has a groove 23. In the embodiment illustrated in Fig. 2, the groove 23 is midway between the opposite edges 24 of the wheel and produces two substantially equal grinding surfaces 25 and 26. As illustrated, the groove 23 is quite deep, being approximately one fourth of the radius of the wheel, and also it will be noted that the groove is rather narrow. The depth and width of the groove may be varied within wide limits, depending upon the material worked upon and the ability of the outer portions of the wheel sections produced by the groove to withstand the disintegrating effect of the centrifugal force developed in the wheel at the necessarily high speeds at which the wheel is operated. It also depends somewhat upon the amount of the wheel which may be worn or dressed-off before the wheel becomes so small that it must be discarded.

In making the grooved wheel of the present invention, one half of the desired quantity of mix is placed in the mold, then semicircular metal spacing plates are placed on top of this, finally the other half of the material is placed on top of the spacing plates, and then the whole is pressed.

Wheels of various grains and compositions may be employed according to the present invention. I have found, however, that a wheel having #16 grits and a binder of phenol condensation products such as Bakelite is quite satisfactory for most grinding operations on rubber and rubberlike products.

By limiting the depth of the groove 23 to that desirable, considering the amount of permissible wear on the wheel, and to that feasible, considering the strength of the binder, the central solid body portion 2'? left intact greatly aids in resisting the disintegrating tendency of the centrifugal force developed in the wheel.

The wheel may be provided with any suitable bushing, such as the lead bushing 28 shown in Fig. 3, to receive the spindle of the driving motor 59 or other drive shaft.

In the use of the wheel of the present invention, as the wheel :3 is traversed over the work represented by the tube 5'! in the embodiment of the invention shown in Fig. 1, and in the direction of the arrow shown thereon, the leading wheel section 25 removes the greater part of the material to be ground-off and in doing so causes some distortion of the material with the resulting roughness and unevenness of the surface. However, as soon as the material reaches the groove portion of the wheel, the stress in the material is relieved causing it to return to its normal position. It is immediately encountered by the trailing section 25 of the wheel, which thereupon removes only the material which has resiliently moved back into place to provide a smooth and even surface. The peripheries of the wheel sections 25 and 26 operate in the same plane, and hence the setting of the Wheel for the desired cut is the same whether the wheel is traversed in the direction of the arrow shown in Fig. 1 or in the opposite direction. When the wheel travels in the opposite direction, the wheel section 25 removes the greater part of the material while the wheel section 26 removes the roughness and chatter marks caused by the then leading section 25.

With the use of the present invention, so little heat is developed as a result of the grinding operation that ones fingers may be held against the work ll close to the portion being engaged without danger of burning and the motor may be touched safely. Upon stopping the wheel l8, it is found that the wheel is not excessively hot. This is of great advantage, for by avoiding excessive overheating of the wheel it, its useful life is greatly extended.

The distance between the opposite edges 24 of the wheel 18 may be substantially the same as that of conventional wheels heretofore used for the same purposes, but, of course, the width of the wheel of the present invention may be increased or decreased if so desired.

If the material being ground is particularly pliable so as to tend to pile up or draw in front of the grinding surfaces of the wheel or if an exceptionally smooth finish is desired, the wheel may be provided with more than one groove 23. For instance, as shown in Fig. 4, the wheel may be provided with two grooves 23a, thus providing wheel sections Zea, 25a and 29. With this arrangement, the material will have two opportunities to become unstressed and return to normal and can be ground three times during a single traverse of the wheel over the work.

In the broader aspects of this invention, the wheel sections need not be integral. They may be formed of two separate wheels 25b and 2% as shown in Fig. 5. In order to provide the resistance to distintegration which is furnished by the body portion 21 of the wheel [8, each of the wheel sections 25?) and 25b may have on its outer side a body portion 2%. In such cases, however, the space provided in the grinding machine to receive the two-part wheel must be enlarged. The wheels may be assembled on a single bushing 23!) and suitable spacing means, such as the washer 38, may be interposed between the adjacent faces of the wheel to produce the desired space 25b between them.

Should the axis of the grinding wheel be antiparallel with the axis of the work, the wheel as a whole may be formed as a section of a cone as shown in Fig. 6, with the operating surfaces of the wheel sections 250 and 250 being located in the same plane indicated by the line 3|.

Other arrangements of Wheel surfaces may, of course, be employed in the use of the present invention to carry out the method herein disclosed of grinding a surface by one wheel section, relieving the article being ground of contact with the wheel to relieve stresses in the article and permit its return to normal, and then grinding off any irregularities, unevenness or roughness developed on the surface of the article as a result of the relief of such stresses.

Variations and modifications may be made within the scope of this invention and portions of the improvements may be used without others.

I claim:

1. The method of grinding rubber-like articles which includes the steps of adjusting a rotating grinding Wheel to take a cut of desired depth in a rotating article; feeding the wheel along the article, the article being relieved of grinding stress at a place between leading and trailing sections of the wheel which have a straight-line contact with a tangential plane.

2. The method of grinding rubber-like articles which includes the steps of rotating an article; contacting the article with a grinding wheel having a straight line contact with a tangential plane parallel to the axis of rotation of the article to take a cut of desired depth while feeding the wheel along the article, the article being relieved from contact with the wheel intermediate the edges of the wheel, and again immediately contacting the wheel with the article as the wheel travels therealong.

3. The method of grinding rubber-like articles with a wheel having a straight line contact with 'a tangential plane which includes the steps of contacting the work with a leading section of the wheel to take a desired out while feeding the wheel along the article; and contacting the article with a trailing section of the wheel which is in substantially the same plane of contact as the leading section and spaced from the latter by a gap, the article opposite the gap being relieved of grinding pressure from the wheel.

4. The method of grinding rubber-like articles with a wheel having a straight line contact in a tangential plane which includes the steps of taking a full depth cut with the leading section of the wheel while feeding the wheel along the article, and finish-cutting the surface with a trailing section of the wheel, the article being relieved of grinding pressure immediately after the first cut by the leading section of the wheel.

CLARENCE GUMPER. 

